Excavators often use hydraulically powered linear and rotary actuators to drive relative movement of various linkages and rotating joints of the excavator. Typically, the linear actuators are hydraulic cylinders and the rotary actuators are hydraulic motors. The hydraulic cylinders and motors can be controlled by a control system. The control system can be operated by an operator. The operator can thereby operate and control the excavator including the hydraulic cylinders and motors of the excavator.
Many conventional excavators control the hydraulic cylinders and/or motors by throttling hydraulic fluid flow to and/or from the hydraulic cylinders and/or motors. The throttling typically wastes energy by converting energy of the hydraulic fluid flow at a pressure into heat energy. This heat energy often must be removed by a cooling system of the excavator. This wasted heat energy increases the power consumption (e.g. fuel consumption) of the excavator.
Many conventional excavators dissipate inertial energy in the relative movement of the linkages and across the rotating joints by throttling hydraulic fluid flow to and/or from the hydraulic cylinders and/or motors. This throttling also typically wastes energy by converting the inertial energy of the relative movements into heat energy via the hydraulic throttling. This heat energy also often must be removed by a cooling system of the excavator. This heat energy also originates as power consumption (e.g. fuel consumption) of the excavator.
Electrical hybrid systems have been developed to assist in recovering energy. However, such systems can be fairly expensive and reliance on complex electrical/electronic based systems having high voltage energy storage can raise serviceability and reliability issues.
Systems such as the one disclosed at U.S. Pat. No. 7,908,852 use hydraulic accumulators to store and re-use hydraulic potential energy. However, such systems rely primarily on throttling valves to provide decelerations thereby reducing the overall efficiency of the systems.